curl_multi_perform - reads/writes available data from easy handles
#include <curl/curl.h>
CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles);
This function performs transfers on all the added handles that need attention in
a non-blocking fashion. The easy handles have previously been added to the
multi handle with
curl_multi_add_handle(3).
When an application has found out there's data available for the multi_handle or
a timeout has elapsed, the application should call this function to read/write
whatever there is to read or write right now etc.
returns as soon as the reads/writes are done. This function does not require
that there actually is any data available for reading or that data can be
written, it can be called just in case. It will store the number of handles
that still transfer data in the second argument's integer-pointer.
If the amount of
running_handles is changed from the previous call (or is
less than the amount of easy handles you have added to the multi handle), you
know that there is one or more transfers less "running". You can
then call
curl_multi_info_read(3) to get information about each
individual completed transfer, and that returned info includes CURLcode and
more. If an added handle fails quickly, it may never be counted as a
running_handle. You could use
curl_multi_info_read(3) to track actual
status of the added handles in that case.
When
running_handles is set to zero (0) on the return of this function,
there is no longer any transfers in progress.
When this function returns error, the state of all transfers are uncertain and
they cannot be continued. should not be called
again on the same multi handle after an error has been returned, unless first
removing all the handles and adding new ones.
int still_running;
do {
CURLMcode mc = curl_multi_perform(multi_handle, &still_running);
if(!mc && still_running)
/* wait for activity, timeout or "nothing" */
mc = curl_multi_poll(multi_handle, NULL, 0, 1000, NULL);
if(mc) {
fprintf(stderr, "curl_multi_poll() failed, code %d.\n", (int)mc);
break;
}
/* if there are still transfers, loop! */
} while(still_running);
Added in 7.9.6
CURLMcode type, general libcurl multi interface error code.
This function returns errors regarding the whole multi stack. Problems on
individual transfers may have occurred even when this function returns
CURLM_OK. Use
curl_multi_info_read(3) to figure out how
individual transfers did.
Most applications will use
curl_multi_poll(3) to make libcurl wait for
activity on any of the ongoing transfers. As soon as one or more file
descriptor has activity or the function times out, the application calls
.
curl_multi_cleanup(3),
curl_multi_init(3),
curl_multi_wait(3),
curl_multi_add_handle(3),
curl_multi_fdset(3),
curl_multi_info_read(3),
libcurl-errors(3)